Variable displacement fuel pump



March 5, 1940.

J. P. JOHNSON VARIABLE DISPLACEMENT FUEL PUMP V 3 Sheets-Sheet 1 Filed Aug. 19, 1938 I March 5, 1940. J. P. JOHNSON VARIABLE DISPLACEMENT FUEL PUMP Fi 19' 1938 3 Sheets-Sheet 2 hd MN Q w wr m %m m x a a S: W. Q x m \w I m W M m .2 5 z: 1 MM MW Q Q im Q MK l R Mb & R

J. P. JOHNSON VARIABLE DISPLACEMENT FUEL PUMP March 5, 1940.

Filed 19' 1938 3 Sheets-Sheet 3 atented 5, 1940 UNITED STATES PATENT OFFICE 2.192.600 vamanm DISPLACEMENT roar. PUMP James P. Johnson, smu- Heights, Ohio, assignor, by mesne assignments, to Pump Engineerin: Service Corporation poration of Ohio Cleveland, Ohio, a cor- 'lhisinvention relates to fuel pumps particularly for use on aircraft, although not so restricted, and has for its primary object to provide an improved fuel pump of the rotary vane 5 or blade type having a variable displacement but where the discharged fuel is maintained at predetermined constant pressure regardless of Volume required by the motor.

It is a further object of lthe present invention l to provide, in a fuel pump of the type referred to,

a. pressure responsive means actuated by the pressure of, the discharged fuel in excess of that predeterminately selected whereby the capacity of the pump may be varied.

15 A further object of the present invention is to provide suitable adjustment whereby the capacity of the pump may be varied between substantially no delivery of fuel and its maximum requirement regardless of the rotor speed.

20 Inthe prior types of fuel pumps such as illustrated in my copending applications, Serial No. 10,644, filed March 12, 1935, Serial No. 170,844, filed October 25, 1937, and Serial No. 196,693, flied March 18, 1938, the maximum volume of 25 fuel was handled by the pump, the excess-over that required by the motor being by-passed back m to the inlet side of the pump. It has been found that there are certain objections to by-passing this volume of fuel within the pump in that it 30 tends to increase the temperature of the fuel and additionally, the rotation of the rotor blades in contact with the fuel tends to whip up the latter thereby producing air pockets which may encourage vapor locks at altitudes where this would be objectionable. It is therefore, a further object of the present invention to provide a variable displacement fuel pump which will deliver only that volume of fuel required by the motor regardless of rotor speeds whereby heat- 40 ing and beating of the fuel is eliminated or materially reduced to a negligible amount.

Another object of the present invention is to provide an improved and simple means by which 7 vention consists in the construction and combination of elements hereinafter described and claimed. 55 Referring to the drawings,

be otherwise adapted as will be Figure 1 is an end elevational view of a pump embodying the present invention.

Figure 2 is a top plan view of the pump shown in Figure 1. 4

Figure 3 is a vertical sectional view taken on 5 line 3-3 in Figure 2 and showing the structural features of the pump.

Figure 4 is a vertical sectional view taken on line 4-4 in Figure 2, and showing in further detail the structural features of the pump.

Figure 5 is a transverse sectional view taken on line 5-! in Figure 4 and showing details of the structure.

Figure 6 is a transverse sectional view taken on line 8-6 in Figure 3 and showing in detail the upper side .of the diaphragm.

Figure 7is. a transverse sectional view taken on line 1-1 in Figure 3 and showing in detail the under side of the diaphragm.

In the drawings, I have illustrated one type of fuel pump embodying the present invention, the structural details of which have been tried and successfully tested, but the invention may apparent to those skilled in the art.

The fuel pump comprises a housing generally designated by the numeral l0, preferably consisting of a casting of aluminum or other desirable iight weight material. The housing is provided with an axially disposed bore ll extending inwardly from one end thereof and terminating in a transverse wall If. The housing In is further provided with an integral portion l3 of reduced diameter which extends outwardly and axially of the bore II, the portion It being provided git its outer end with a laterally extending flange ll by means of which the pump may be suitably attached to the motor or other driving means. The portion I; has an axially disposed opening I! communicating at one end with the bore H and at its opposite end with an interiorly screwthreaded bore l6 of larger diameter which extends inwardly from the flange l4 providing an abutment or seat II. The housing I0 is also provided with a pair of outwardly projecting bosses I. on diametrically opposite sides thereof which are provided with interiorly screwthreaded pipe tap openings l9 and 20 communicating with the bore ll. These openings l9 and 2| function as fuel inlet and outlet openings and are adapted for connection with the fuel supply tank and carburetor respectively.

A bushing 2| of bronze or other suitable material is rigidly mounted within the housing l0 and comprises a tubular portion 22 disposed within the opening l5 and a laterally extending peripheral flange 23 in abutting engagement with the wall l2and the adjacent peripheral surface of the bore l, the inner face of the flange 23 being smooth and flat and providing one end wall of the pumping chamber. An outer sleeve or liner 24, of bronze or other suitable material, is rigidly secured within the bore II and has one end in abutting engagement with the inner face of the flange 23. The sleeve 24 has a circular opening 25 extending therethrough, the axis of which is eccentric to, slightly below but parallel with the axis of the bore II, as more clearly shown in Figure 4. The sleeve 24 is further provided with one or more openings 25 and 21 which extend transversely through the wall thereof on diametrically opposite sides in communication'with the inlet and outlet openings l9 and.28 respectively.

An inner cylindrical sleeve 28, of steel or other suitable material, has a smaller outside diameter than the diameter of the opening 25 in the outer sleeve 24 and is disposed within the latter for relative adjustment for a purpose to be later described. Thesleeve 28 abuts at one end with the inner face of the flange 23 and its outer end' aligns with the outer end of the outer sleeve 24, as more clearly shown in Figure 8. The inner peripheral surface of the inner sleeve 28 forms the outer wall of the pump chamber and one or more openings 29 and 30 extend transversely through the wall thereof on diametrically opposite sides in communication and preferably in alignment with the openings 26 and 21 respectively in the outer sleeve 24. A cover plate 3| has a circular portion 32 adapted to fit snugly within the open end of the bore II and a lateral flange 33 detachably engageable with the'adjacent portion of the housing II). A rubber gasket 34 is disposed between the flange and housing to provide a seal and a plurality of machine screws 35fproject through openings in the flange 33 and are secured in screwthreaded aligned openings in the housing. The cover plate 3| is further provided with an axial bore 38 on itsinner side in axial alignment with; and of the samediameter as the opening |5 in the portion-|3 of the housing. A bushing 31, of bronze or'other suitable material, and similar to the-bushing 2|, is securely mounted on the cover plate and has'a cylindrical extension 38 disposed within the bore 36 and a laterally extending circular flange 39 on the inside of the portion .32. The inner face of the flange 39 is flat and smooth, in parallelism with the face of the flange 23 and engages the outer endsof the outer sleeve 24 and inner sleeve 28 to maintain them in assembled relation.

A rotor 48, of steel or. other suitable material, is rotatably mounted in the housing andcomprises a circular body portion 4| of smaller diameter than the inner diameter of said inner sleeve 28 within which the body portion is eccntrical ly disposed and outwardly projecting axial extensions 42 and 43 which are rotatably mounted in the adjacent bushing extensions 22 and. 38 respectively. The rotor is further provided with an axial opening 44 of substantial diameter which extends entirely through the extensions 42 and 43 and body portion 4| within which a tubular roller member 45 is freely disposed. The body portion 4| of the rotor is provided with a plurality of radially disposed slots 46 which extend longitudinally throughout its length and within which are slidably mounted a plurality of blades or vanes 41, the outer ends of which have running engagement with the inner peripheral surface of the inner sleeve while the opposite ends have running engagement with the adjacent faces of the flanges 23 and 39 respectively. The inner ends of the blades 41 project into the opening 44 within the body 4| and are engageable with the roller member 45 which maintains the blades in their proper running position. Six blades are here shown which improve the evenness of flow of the discharged fuel but any other number may be employed to advantage.

In order that the capacity of the pump may be varied the inner sleeve 28 is madeadjustable for this purpose. The sleeve 28 is provided with a pair of radial integral projections 48 and 43 on diametrically opposite sides which slidably fit within complementary grooves 5|] and 5| formed upon the inner wall of the outer sleeve 24, as more clearly shown in Figure 4. The grooves are of sufllcient depth to permit the required movemer t of the inner sleeve to vary the capacity of .ing in the housing l0 and its inner end projecting through an aligned opening in the outer sleeve into engagement'with the adjacent end of the projection 48, shims 53 being used to'obtain the proper adjustment. The axis of the opening 25 in the outer sleeve 24 is fixed as is the axis of the rotor 40, these axes being relatively eccentric but in a common vertical plane, as shown in Figure 4. ,The axis of the inner sleeve 28 is likewise in the same vertical plane as the aforesaid axes but its relative position varies by reason of the restricted movement of the inner sleeve 28 to positions in engagement with the inner peripheral wall of the outer sleeve at diametrically opposite points and any position therebetween. The relative positions of the various parts shown in Figure 4, effect the maximum capacity of the pump in which the portion 4| of the rotor 40 has a close running engagement with the inner peripheral wall of the inner sleeve 28 at its upper portion. By increasing this clearance the capacity of the pump is lowered and may be decreased to' zero or by moving the inner sleeve to its uppermost position, wherein the portion 4| of the rotor '40 has a close running fit with the inner'peripheral surface in which position a diametrically opposite slightpressure is created in the direction of the inlet side of the pump. In other words any desired exact volume of fuel may be obtained by the adjustment provided for by the adjustment of this inner sleeve.

The adjustment of this inner sleeve may be accomplished in any desirable manner but preferabbr by means of fluid pressure as shown' in the drawings. The housing I0 is further provided with a second integral laterally extending portion 54 terminating in a dish shaped portion 55 having a marginal flange 58 the upper surface of which provides a seat. The portion 54 is provided with an axial opening 51 within which a tubular plunger or stem 58 is slidably disposed. TheJower end of the stem is closed and formed with a reduced portion 59 which projects freely through an aligned opening in the outer sleeve '24. The extreme lower end 60 of the stem is exteriorly screwthreaded and securely threaded into an aligned screwthreaded opening in the projection 48 on the inner sleeve 28 by means of which the latter may be moved. The stem is further provided with a lateral flange 6| extend-' dil is in communication'with the atmosphere through connect the upper side of the diaphragm with the ing circumferentially thereabout and positioned outwardly of the dish shaped portion 55, the stem being exteriorly screwthreaded therebeyond. A disc 62, preferably of steel, has an axial opening fitting over the outer end of the stem and resting upon the outer side of the flange Bi and within the dish shaped portion but spaced therefrom. The disc should be as large as possible so as to be more sensitive to the pressure which actuates it and its outer marginal edge may be turned downwardly at M. A fiat flexible diaphragm 6i, preferably of rubber and fabric composition, is disposed above the disc 62 and has an opening through which the stem projects The marginal edge portion of the diaphragm M rests upon the seat of the flange 5B and is securely clamped by a marginal flange 65 on a cover member 66. The cover member 66 is detachable by means of a plurality of machine screws ti which extend through aligned openings provided in the flanges 5t and t5 and the adjacent portion of the diaphragm and which screws are threadably secured in the flange at to provide a sealed joint. A disc 68, oi steel or other suitable material, is positioned upon the outer side of the diaphragm M, and has a diameter slightly greater than that of the disc t2 but not as great as the exposed marginal portion of the diaphragm. The outer edge of the disc 88 may be turned outwardly at M to provide a rounded corner for engagement with the diaphragm to prevent injury to the latter and the disc has an axial opening through which the outer end of the stem projects. A nut ill is screwed onto the outer end of the stem into rigid engagement with the disc M for securely maintaining the discs and diaphragm in assembled unitary relation and in abutment with the flange ti. To permit discharge of the fuel at a predetermined selected pressure and to. thereafter maintain a constant pressure of the discharged fuel, a coiled spring H is used which has a portion disposed within the tubular stem 58 with its lower end in engagement with the closed end of the stem. The upper end of the spring ii projects beyond the stem and is freely disposed within an axial interiorly screwthreaded opening 12 provided in an extension it of reduced diameter formed integrally on the outer side of the cover member 68.

An exteriorly screwthreaded plug M is threadablymounted in the opening it and engageable with the outer end of the spring ii.- for tensioning the latter to thereby exert a pressure upon the closed end of the stem whereby the inner sleeve 29 is yieldably maintained in its lowermost position. Any means may be employed for adjusting the plug axially within its openig but a simple means embodies a thumb knob 15 having a lateral flange it adapted to engage the outer end of the extension i3 and a depending non-circular stem 11 projecting freely through a complementary noncircular opening provided in the plug 14. Thus by turning the knob the plug may be threaded inwardly or outwardly as desired until the spring is properly tensioned. The adjustment may be maintained by a bonnet-like nut 18 having an opening through which the knobproiects and threaded upon the extension 13 into clamping engagement with the flange 16 on the adjusting member. The upper side of the diaphragm 64 a small opening 19 in a plug 90 which is exteriorly screwthreaded and threadably removably in a screwthreaded opening provided in thecover member 66. In some instances it is desirable to supercharger in which event the plug 90 is removed and a pipe line is connected therefrom.

1 As heretofore stated a further important function of the pump is to deliver any volume of fuel 5 required by the motor regardless of rotor speed and while this is accomplished mechanically by means of the movable inner sleeve the movement of the latter is automatically efiected by the pressure of the discharged fuel in excess of that 10 desired. .The housing In is therefore, provided with a passageway 82 which has one end in communication with the discharge side of the pump. or outlet opening 20 and its other end in communication with the under side of the diaphragm 15 M. To render the pump operable in either direction, a second passageway 83, similar to the passageway 82, is provided in the opposite side of the housing Ni andhas one end in communication with the inlet side of the pump or inlet opening 2i) l9 and its other end in communication with the under side of the diaphragm. With this adaptation one of the passageways must be closed depending upon the direction of rotation of the rotor. With the rotor rotating in a clockwise direction as shown in Figure 4 the passageway 93 is closed and any suitable means may be employed. However, a simple and emcient means consists in the provision of diametrically disposed bores M and 85 which extend inwardly fromv opposite sides communicating with the passage-' ways 82 and 83 respectively. Inserts 86 and t! fit snugly within but are removable from the bores 92 and t3 and the insert 86 isprovided with a reduced portion at adjacent the passageway 82 to 3 permit unrestricted flow of fuel through the latter. The outer ends of the bores are interiorly screwthreaded and plugs '89 are removably mounted therein to prevent accidental displacement of the inserts, the latter being provided on opposite ends i with interiorly screwthreaded openings by means of which the inserts may be removed by the use of a suitable implement. Furthermore the bores and inserts are of identical size so that in order to change the direction of operation of the pump only the position of the inserts are reversed from that shown in Figure 4.

The rotor may be driven by any suitable means but preferably as shown in Figures 3 and 5. A drive shaft 90 is disposed ci'incentrically of the Bil axis of the rotor and has a circumferential flange 9i rotatably mounted in the adjacent end of the bushing extension 22. The shaft is further provided with a tongue 92 on its inner end which extends transversely and projects into aligned complementary recesses in the adjacent end of the rotor extension 42 for imparting rotation to the rotor. The outer end of the shaft 99 projects outwardly beyond the attaching flange l4 and is provided with splines 93 adapted for operative 60' connection with the motor or other power source.

A retainer member 94, preferably of aluminum material, is exteriorly screwthreaded at its outer portion and removably mounted in the threaded bore l6 adjacent the flange ll. The retainer 35 member 94 also has a portion 95 of reduced diameter which terminates in a lateral flange 96 in abutting relation with the seat T. A gasket 91 is disposed between the flange 96 and the seat l'l-to I provide an efiective seal against the escapeof oil. The inner end ofthe retainer member 94 is further provided with an axial bore 88 communicating at its inner end with an axial bore. 99 of! slightlysmaller diame rproviding an axially disposed flange I exte ding circumferentially 75.

about the adjacent portion of the shaft. A metal seal disc I0! is mounted within the bore 98 for slight axial movement and in abutting engagement with the adjacent end of the flange 9|, the

opposite side being in spaced relation to the bottom of the bore 98. A resilient seal ring I02 of rubber and fabric composition, is disposed within the bore 99 the opposite sides abutting the bottom of the bore and the ring respectively and encircling the fiange I00. This construction provides a yieldable sealagainst the leakage of oil. The retainer member 94 is further provided with a cored chamber I03 encircling the shaft and passageways I04 providing communication between the chamber and the reduced portion 95 at diametrically opposite sides as more clearly shown in Figure 5. A plurality of radially disposed passageways I05 are provided in the extended portions I3 of the housing which communicate at one end with the reduced portion 95 of the re tainer member and at their other end with pipe taped openings I06 normally closed by means of screwthreaded plugs I01. These'ccmmunicating pasageways are provided so that any oil which is taken up by the drive shaft and released by.

rotation will be led away from the pump elements and may be drained oil? by the removal of one of the plugs I01. The retainer member 94 is normally maintained in proper position by means of a bolt I08.

The oil seal is effectively maintained by the pressure created in the pump which exerts an outward force upon the flanged end of the shaft 90 and consequently the disc IOI thus compressing the ring I02. In the event that there is insuflicient pressure within the pump, as in start ing etc., the seal is nevertheless normally effective by utilizing the tubular roller member 45 as more clearly shown in Figure 3. The closed end of the roller member 45 abuts the adjacent end of the tongue 92 on the shaft 90. A coiled spring I00 is disposed within the roller member and has one end in engagement with the closed end thereof while its other end engages a pin II 0 slidably mounted in the open end of the roller member. The pin IIO has a portion projecting outwardly terminating in a head III which abuts the bottom of the bore 36. This spring I09 may be predeterminately selected so as to exert the desired pressure on the closed end of the roller member which in turn suitably compresses the ring to' prevent leakage.

In the operation of the pump, with the elements in their relative position shown in the drawings and the rotor being driven, by the motor, in a clockwise direction as indicated by the arrows in Figure 4, the inlet opening I9 is connected with the fuel supply tank and the outlet opening 20 is connected with the carburetor which in turn is connected with the motor in a manner well through the outlet opening 20 in a manner well known.

It will be understood, of course, that the capacity of the pump varies almost in direct propor v tion to the R. P. M. of the rotor where close clearances and tolerances are maintained, and conse- T quently the pump would, under ordinary circumstances, be required to handle a volume of fuel greatly in excess of that required by the motor, as will be more apparent from a study of my copending applications heretofore referred to. To maintain the relation between fuel consumed by the motor and fuel handled by the pump, any increase in pressure of the discharged fuel in excess of that desired, is transmitted to the under side of the diaphragm 64- and disc 62 causing the latter to be raised and with it the inner movable sleeve 28 in opposition to the tensioned spring I I. This movement of the sleeve 20 increases the running clearances between the body portion 4| of the rotor and theupper inner peripheral surface of the sleeve 28, as viewed from Figure 4, thereby reducing the capacity of the pump to a point where the volume of fuel handled thereby is substantially equal to that required by the motor regardless of the rotor speed. As the maximum displacement of the pump is many times greater than the required displacement, the screw 52 is provided for predete'rminately effecting the minimum running clearance between the body portion M of the rotor and the inner peripheral surface of the sleeve 28. This automatic operation is made possible by closing off the passageway 83 by means of the removable insert 81 and the pump may be operated in a reverse direction by through and additional openings for cooperation with said inlet and outlet openings, a rotor rotatably mounted in said housing about a fixed axis eccentric to the axis of said circular opening and positioned within said sleeve and having a portion normally in running engagement with the inner peripheral surface of said circular opening, said rotor having reciprocal blades adapted for drawing fuel into the inlet opening and discharging the same under pressure from the outlet opening, means in said housing sensitive to minute variations through a wide range of I changes in surrounding atmospheric pressures for adjusting said sleeve to vary the eccentricity of said rotor relative to said sleeve in response to changing surrounding atmospheric pressures whereby to cause said pump to deliver a constant pressure at said outlet opening irrespective of said changing pressures, said means including a flexible disc-like diaphragm in communication on the outer side thereof with the atmosphere through a small opening formed in said housing and in communication on the inner side thereof with said outlet opening, whereby outlet fluid pressure acts to urge said sleeve in the direction of least eccentricity, and resilient means for urging said sleeve in the direction of greatest eccen-. tricity with a predetermined force.

2. In a pump adapted for supplying fuel to the charge-forming device of an aircraft said pump being capable of'delivering said fuel at a constant delivery pressure irrespective of v inlet pressures said pump comprising a housing having fuel inlet and outlet openings, a sleeve formed with a circular opening therethrough mounted in said housing for adjustment transversely to thelaxis of said circular opening said sleeve being formed with additional openings for cooperation with said inlet and outlet openings, a rotor rotatably mounted in said circular opening about a fixed axis, said rotor having reciprocal blades carried thereby arranged for drawing fuel from said inlet opening and for discharging the same from said outlet opening, means in said housing being sensitive to minute variations through a wide range in surrounding atmospheric pressures for adjusting said sleeve relative to said rotor to vary the eccentric relation between the axis of said rotor and the axis of said sleeve for varying the difference between said inlet and said delivery pressures, said means comprising a flexible disc-like diaphragm sealably connected at its periphery with said housing and provided with means connecting the central portionthereof with said sleeve, said housing being formed with a passage placing the underside of said diaphragm in communication with said pump outlet and with a second passage of smaller size placing the upper side of said diaphragm in communication with the atmosphere and means for urging said sleeve in the direction of its greatest eccentricity relative to said rotor with a predetermined force, whereby the surrounding atmospheric pressure changes are made to affect the upper side of the diaphragm thus causing said eccentricity varying means to vary said eccentricity to produce a constant delivery pressure.

3. In a variable displacement fuel pump for aircraft, a housing having fuel inlet and outlet openings, a sleeve movably mounted in said'housing and having a circular opening extending therethrough, said sleeve being formed with additional openings therethrough for cooperation with said inlet and said outlet openings respectively, a rotor rotatably mounted in said housing about a fixed axis eccentric to the axis of said circular opening and positioned within said sleeve and having a portion normally in running engageinent with the inner peripheral surface of said circular opening, said rotor having reciprocal blades adapted for drawing fuel into the inlet opening and discharging the same under pressure from the outlet opening, means in said housing connected to said sleeve effective to adjust the same to vary the eccentricity thereof relative to said rotor, comprising resilient means for urging said sleeve in the direction of greatest eccentricity with a predetermined force, means defining a chamber adjacent said rotor pumping means, means including a flexible disc-like diaphragm dividing said chamber into a first compartment and. a second compartment, a threaded opening in the wall of said second compartment adapted to be placed in communication with a source of variable fluid pressure, a first passage formed in said housing adapted to place said first compart; ment in communication with said pump outlet, a second passage formed in said housing adapted to place said first compartment in communication with said pump inlet, threaded openings formed in said housing and intersecting each of said passages, a first threaded closure means arranged to fit each of said last named threaded openings and permitting fiow thereby through the associated male, as second threaded closure means arranged to fit each of said last named threaded the associated passage. whereby the direction of operation of said pump may be reversed merely by interchanging said threaded closure means,

and constant delivery pressure is obtained irrespective of the direction ofv operation of said pump.

4. In a variable displacement fuel pump for aircraft, a housing having fuel inlet and outlet openings, a sleeve movably mounted in said housing having a generally circular opening extending therethrough and having additional openings for cooperation with said inlet and outlet openings, a rotor rotatably mounted in said housing about a fixed axis normally eccentric to the axis of said circular opening andpositioned within said sleeve and having a portion normally in close running association with the inner peripheral surface of said sleeve, said rotor having reciprocal blades adapted for drawing fuel into the inlet opening and discharging the same under pressure from the outlet opening, means in said housing sensitive to minute variations through a wide range of changes in surrounding atmospheric pressures for adjusting said sleeve to vary the eccentricity of said rotor relative to said sleeve in response to changing surrounding atmospheric pressures whereby to cause said pump to deliver a constant pressure to said outlet opening irrespective of said changing pressures, said means including a flexible disc-like diaphragm and means placing the same in communication on one side thereof, at least indirectly, with the atmosphere and in communication onthe other side thereof with said outlet opening, whereby outlet fluid pressure acts to urge said sleeve in the direction of least eccentricity and resilient means for urging said sleeve in the direction of greatest eccentricity with a predetermined force, said arrangementbeing further particularly characterized by the provision of a hollow stem passing through the a central portion of said diaphragm andzclosed at the lower end thereof and connecting said sleeve with said diaphragm, said resilient means comprising a long helical spring positioned within said stem and engaging said closed end thereof and means engaging the other end of said spring above said diaphragm for adjusting the compression thereof.

, 5. In a variable displacement fuel pump for air craft, a housing having fuel inlet and outlet openings, a sleeve movably mounted in said housing having a generally circular opening extend ing therethrough and additional openings for cooperation with said inlet and outlet openings, a rotor rotatably mounted in said housing about a fixed axis normally eccentric to the axis of said circular opening and positioned within said sleeve and having a portion normally in close running partment, an opening formed in the wall of said second compartment adapted to communicate with a supercharger outlet, means defining a passage placing said first compartment and the mined force, said arrangement being sensitive to minute variations through a wide range of changes in the pressures to which said diaphragm is subjected.

JAMES P. JOHNSON. 

